The cooling-water control valve device is known in the art for controlling a flow rate of cooling water for the internal combustion engine (hereinafter, the engine). For example, in the cooling-water control valve device (hereinafter, the water valve device) disclosed in Japanese Patent Publication No. 2016-188702, a valve member of a main valve unit is rotatably provided in a main valve accommodation space for controlling the flow rate of the cooling water to be supplied to the engine.
The water valve device of the above prior art has a fail-safe valve unit provided in a fail-safe valve accommodation space. The fail-safe valve accommodation space is communicated to the main valve accommodation space and a main water passage, through which the cooling water flows from the main valve accommodation space to an outside of the water valve device (for example, a radiator). When temperature of the cooling water is lower than a predetermined value, the fail-safe valve unit is closed so as to block off flow of the cooling water from the fail-safe valve accommodation space to the main water passage. On the other hand, when the temperature of the cooling water is higher than the predetermined value, the fail-safe valve unit is opened so as to allow the flow of the cooling water from the fail-safe valve accommodation space to the main water passage. When the main valve unit becomes unable to rotate in the main valve accommodation space, the flow of the cooling water from the main valve accommodation space to the radiator via the main water passage is blocked off. Then, the temperature of the cooling water is increased. When the temperature of the cooling water becomes higher than the predetermined value, the fail-safe valve unit is opened so as to supply the cooling water (the temperature of which is increased by the engine) to the radiator through the fail-safe valve unit. As above, it is possible to prevent a possible over-heat of the engine, even when the main valve unit becomes unable to rotate.
In the above water valve device, the fail-safe valve accommodation space is communicated to the main valve accommodation space. In a case that extraneous material enters the main valve accommodation space and the main valve unit is locked by such extraneous material, the main valve unit may be broken in the main valve accommodation space. Then, a broken piece of the main valve unit may enter the fail-safe accommodation space and the broken piece may be adhered to a valve portion of the fail-safe valve unit. In such a case, functional failure may occur in the fail-safe valve unit.